[dba-VB] C# Databases without borders

I want to build a little application where I have a very simple zip code table of about 40 thousand 
zip codes, with things like household count, population count, lat and long.  My application would 
take lists of zip codes and sum the population and household counts, count the zips etc and put a 
count on the screen in a table format.

I already do this using SQL Server to hold the zip code table.  I get the zip lists into csv files, 
then create a table inside of SQL Server, join on the zip code and sum the population and household 
counts.

Now I want to build an application to do this but SQL Server is way overkill.

Can I use a csv or even xml to hold the zip table, create an xml table to hold the zip lists entered 
by the user and so forth.  IOW I need a low impact alternative to SQL Server.  Even express is just 
way overkill for this.

Somewhere in the back of my mind I am thinking that ADO.net knows how to load tables, create 
relationships between tables, enforce the join etc.  IOW do the store entirely in XML and just use 
ADO to do the rest.

Is this possible?  Would the speed be acceptable for a join between tblZipMaster and tblZipUserXyz 
on Zip count(zip) sum(household) etc. directly in memory.
-- 
John W. Colby
www.ColbyConsulting.com